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  • Starting ABM algorithm

Starting ABM algorithm · Changes

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Update Starting ABM algorithm authored Apr 06, 2022 by Gabriel Wlazłowski's avatar Gabriel Wlazłowski
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Starting-ABM-algorithm.md
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......@@ -5,14 +5,14 @@ f(y,t) \equiv \dfrac{1}{i}(\hat{H}(\{\varphi_n\},t)-\langle H\rangle_n)\varphi_n
for four time steps back: $`f_{k-1}`$, $`f_{k-2}`$, $`f_{k-3}`$, $`f_{k-4}`$.
# Starting from a stationary state
In the case of a stationary state, $`\varphi_n`$ are eigenstates of the hamiltonian, and the instantaneous quasi-particle energies are equal to quasiparticle energies $`E_n=\textrm{const}`$. Then, as long as the hamiltonian does not depend we obtain:
In the case of a stationary state, $`\varphi_n`$ are eigenstates of the hamiltonian, and the instantaneous quasi-particle energies are equal to quasiparticle energies $`E_n=\textrm{const}`$. Then, as long as the hamiltonian does not depend on the time we obtain:
```math
f_{k-1}=f_{k-2}=f_{k-3}=f_{k-4}=0
```
To use this prescription for initialization of ABM algorithm you need to select in the input file:
To use this prescription for initialization of ABM algorithm, you need to select in the input file:
```bash
selfstart 0 # use Taylor expansion for first 5 steps?
selfstart 0 # use Taylor expansion for the first 5 steps?
```
......@@ -21,9 +21,9 @@ In this case, we need to generate the first five steps using single step method.
```math
\varphi_n(\bm{r},t+\Delta t) = e^{-i(\hat{H}(\{\varphi_n\},t)-\langle H\rangle_n)\Delta t}\varphi_n(\bm{r},t)\approx \sum_{k=0}^{4}\frac{(-i\Delta t)^k}{k!}(\hat{H}(\{\varphi_n\},t)-\langle H\rangle_n)^k\varphi_n(\bm{r},t)
```
where we expanded the evolution operator into Taylor series up to the same order as the precision of the ABM algorithm.
where we expanded the evolution operator into the Taylor series up to the same order as the precision of the ABM algorithm.
In order to use the Taylor expansion method for the generation of the first five steps you need to select in the input file:
To use the Taylor expansion method for the generation of the first five steps, you need to select in the input file:
```bash
selfstart 1 # use Taylor expansion for first 5 steps?
```
\ No newline at end of file
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